Shipment of cargo often occurs via containerized units, i.e., cargo containers. Pre-loaded containers offer handling efficiency and security during transportation. As compared to individual handling of multiple items on site at the transportation medium, containers are more easily and conveniently loaded apart from the medium, delivered to the medium where they are rapidly and efficiently loaded as a single unit and later, similarly unloaded at their respective destinations. The containers also offer security from theft, protection against handling damage and weather for the cargo while en route. Originally, container openings were typically covered by rigid doors to provide conventional sealing and safeguards against cargo shifting, weather, etc. Many problems are associated with rigid doors, for example: Differing flexing tolerances of the doors versus tolerances of the container bodies tend to result in door or frame warpage, destroying sealing integrity and even use of the doors themselves, thereby putting containers out of service and impeding their revenue generating value. Consequently, increased use of fabric doors or covers has evolved to reduce container unit costs, such as those related to purchase, maintenance, and shipping weights. In the known art, many fabric covers/doors incorporate one, two, or even three horizontal rigid bars, with the bottom bar, typically incorporating a latching device such as a spring-loaded bolt action slide within the bar itself or within the container opening side support. These door bars and the associated latching devices cause an inordinate amount of damage, for example: If the bottom bar is not properly secured, the door will flap and swing over the container when towed, spearing holes in the top of the door and possibly bending the bar or locking bolt. Bars/latches tend to jam in the closed position. To gain access to the inside of such containers, it is not uncommon to slash the door canvas or force forklift tines under the bar and jerk it open, often bending the bar, the lock bolt, or the container side brace, any of which will take a container out of service.
Along with bars, some fabric covers/doors incorporate tension springs located in pockets sewn onto the covers. When the bottom bar is unlatched, the cover is supposed to automatically roll up and out of the way for container loading. These covers offer even more problems than bar doors without tension springs and tend to be more expensive. The springs will tend to lose tensile strength or to become twisted, resulting in the door rolling only part way up, thereby blocking access to the interior of the container and leading to increased loss of container service and maintenance. Furthermore, if the bottom bar is not secured and the door swings over the container while being towed, damage to the container and the door itself is exacerbated.
Other container covers, most closely related to this invention, are of fabric without bars, but they incorporate elaborate, complicated, and costly devices for securing the covers to the container. Such containers typically incorporate a multitude of tensioning devices, interconnected with a series of fabric cross-webbing. Multiple tensioning devices increase handling time during door opening and closing, and amplify the amount of maintenance required. Tensioning patterns tend to be more complicated than necessary and/or involve individual segments. Hooking mechanisms on these covers tend to be flimsy, difficult to engage, or subject to excessive maintenance. Fabric strapping also tends to increase tensioning device wear and tear and subsequent maintenance due to chafing against metal corner points. Outstanding in the prior art is the following.
______________________________________ PRIOR ART INVENTOR DATE U.S. Pat. No. DESCRIPTION ______________________________________ Nordstrom Sept. 6, 1977 4,046,186 Cargo Container Opening Cover Looker Sept. 3, 1985 4,538,663 Cargo Container Dunwoodie Jan. 3, 1989 4,795,047 Container and Construction Bretschneider Sept. 7, 1993 5,242,070 Freight Container et al. Brierton Jan. 3, 1995 5,377,856 Air Cargo Security Vault Holland et al. March 7, 1995 5,395,682 Cargo Curtain ______________________________________